The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.
Metal Organic Frameworks (MOFs) (also known as coordination polymers) are an emerging class of hybrid crystal materials where metal ions or small inorganic nano-clusters are linked into one-, two- or three-dimensional networks by multi-functional organic linkers. They have many appealing features having surface areas of thousands of square meters per gram, extremely low density, interconnected cavities and very narrow porosity distributions. A variety of open micro- and mesoporous structures can be developed, leading to materials with extreme surface area. Moreover, the possibility to arbitrarily engineer the cavities' architecture and the pores' surface chemistry makes metal organic frameworks excellent candidates for a wide variety of applications, from gas storage/separation to catalysis, drug delivery, optoelectronics and sensing.
Metal Organic Frameworks are also an emerging class of adaptive materials because they respond to external stimuli (light, electrical field, presence of particular chemical species), promising new advanced practical applications.
There are a large number of studies of the chemical structure and properties of metal organic frameworks. However, the applicants have only found a small number of studies investigating metal organic framework crystallisation mechanism. These studies suggest that conventional synthesis methods are largely based on the homogeneous crystallisation promoting of secondary building units (SBUs), which in turn join together to form the final crystal structure. Crystal growth can also proceed by a two-dimensional surface crystallisation promoting “birth and spread” mechanism.
Fischer et al (2005) Journal of American Chemical Society, 127, 13744-13745 indicated that the growth of a particular metal organic framework (MOF-5) crystal could be directed on 2D surfaces functionalised with self-assembled carboxy-terminated monolayers (SAMs). In this approach, SBUs or larger MOF-5 nuclei bind to Zn2+ cations coordinated on the carboxylated SAMs via a terephthalate bridge. However, Fischer's research only points the way towards the development of metal organic framework based solid state devices and thin films. Furthermore, for a large scale production purpose the protocol is time-expensive as it requires a remarkable preparation time of more than 100 hours. In addition, the amount of MOF-5 that forms is limited by the planar surface area on which the SAM is deposited.
It would therefore be desirable to provide an alternative metal organic framework synthesis method. Preferably, this method would achieve fast, versatile (independent of substrate properties) and spatially controlled metal organic framework crystallisation.